In many instances, a need exists for controlling the path of cars and trucks. The prior art has devised many means for controlling such vehicles including barriers such as guard rails and crossing gates. Often the intended purpose of such barriers is to protect vehicles from entering secure areas such as government installations or unsafe areas such as construction sites or reversible high-occupancy vehicle lanes. However, in most cases, prior art barriers inflict extremely high deceleration rates on vehicles and can cause extensive damage to the vehicles and the barriers. Further, safety of the driver and passengers in such a vehicle is often compromised. Further, repairing the damage to the barriers can be time consuming and expensive.
Some barrier systems of the prior art have attempted to remedy the problems created by high deceleration rates by devising brakes of various configurations designed to decelerate vehicles relatively slowly. The prior art brakes are designed for dissipating its kinetic energy by translation of that energy into heat by friction.
Of course, the kinetic energy of the vehicle increases with the square of its velocity according to the equation E=1/2 mv2. As the speed of the vehicle doubles, the kinetic energy increases by 4 times. The braking systems must therefore dissipate 4 times as much energy to stop the vehicle and consequently require 4 times the distance to do so. The energy stored as heat is gradually released to the surrounding environment.
Prior art efforts to control the straight line deceleration of vehicles with barrier systems include various types of barriers which incorporate braking mechanisms. U.S. Pat. No. 6,312,188 to Ousterhout, et al. discloses a device and associated method for impeding the motion of a land vehicle traveling along a pathway on a terrain surface. Two opposing supports are positioned at opposite sides of a vehicle path of travel. Each support is capable of being actuated from a compressed condition to an extended condition. A propulsion system actuates the supports. When the supports are compressed, vehicles pass over the barrier unimpeded. When the supports are actuated, the barrier rises to a position in the path of motion of a vehicle. Each support includes a deceleration cable that is wound around an axle system of a brake box. The axle system is comprised of outer and inner nested shafts which include a pawl and ratchet. A spring loaded caliper system applies a constant clamping force to a brake disk. As the deceleration cable is withdrawn from the brake box, the unwinding of the cable rotates the axle and in turn rotates the brake disk via the locked ratchet mechanism. To rewind the deceleration cable around the axle, a rotational force is applied to the axle via a hexagonal nut on the end of the axle. The pawl unlocks and the cable is rewound around the axle without rotating the brake disk. The brake force is applied by a relatively small brake pad thereby reducing the maximum braking force available. Further, the braking force is not adjustable.
U.S. Patent Application Publication No. 2002/0109131A1 to Smith, et al. discloses a braking system that provides a varied braking force to maintain the rate of deceleration of a vehicle at or below a predetermined value. The system includes a guardrail structure and an impact sled positioned ahead of the guardrail structure. The guardrail structure and the impact sled are connected to two guide rails. A braking unit is positioned within the impact sled. When a vehicle collides with the impact sled, the impact sled collides with the braking unit and the guardrail structure is caused to move vertically and fold. Hydraulic pressure builds in the braking unit so that a braking force is applied to the brake rails. A force sensing valve regulates pressure from the braking unit until the rate of deceleration reaches a predetermined value. The system is not physically damaged through use. The disclosed system is costly and mechanically complicated.
U.S. Pat. No. 7,125,197 to Krewsun, et al. discloses a vehicle capture net disposed between a pair of towers each of which includes a shaft, a pair of spools coupled to the shaft, and a pair of straps connected to the net. Each strap is wound on a spool. Unwinding of the straps from the spools advances the pair of spools on threaded portions of a shaft to compress a frictional brake. The degree of compression increases as the strap unwinds, thereby increasing the magnitude of the restraining force as the straps are unwound. An electric motor and clutch assembly releases the brake and rewinds the strap on the spool. The system disclosed is complicated and potentially prone to high maintenance expense.